Fuel oil heat exchanger utilizing heat pipes

ABSTRACT

A heat exchanger includes a heat exchanger housing having a first flow path with a first inlet and a first outlet, and having a second flow path with a second inlet and a second outlet. A first fluid flows from the first inlet to the first outlet in the first flow path, and a second fluid flows from the second inlet to the second outlet in the second flow path. A heat pipe array within the housing extends between the first flow path and the second flow path for transferring heat from the first fluid to the second fluid.

BACKGROUND

The present invention relates to heat exchangers, and in particular, to a heat exchanger utilizing heat pipes.

Heat exchangers typically use shell and tube technology or plate and fin technology. Shell and tube heat exchangers include a large shell with bundles of tubes running through the shell. A first fluid runs through the tubes and a second fluid runs through the shell around the tubes. Heat is exchanged between the first fluid and the second fluid at an interface between the fluids as the fluids flow through the heat exchanger. Plate and fin heat exchangers include layers of corrugated sheets separated by flat metal plates to create a number of finned chambers. A first fluid and a second fluid flow through alternating layers of the heat exchanger. Heat is exchanged between the first fluid and the second fluid at an interface between the fluids as the fluids flow through the heat exchanger.

Heat exchangers utilizing shell and tube technology or plate and fin technology rely on convective heat transfer to transfer heat from the first fluid to the second fluid. Convective heat transfer is the transfer of heat from a warmer fluid to a cooler fluid through movements of the molecules in the fluids. Convective heat transfer includes heat that is transferred both by conduction and advection. Conductive heat transfer includes heat transferred by the diffusion and movement of individual particles within the fluid. Advection heat transfer includes heat transferred by bulk fluid flow of a fluid. The effectiveness of convective heat transfer increases with an increase in the surface area of the interface between the first location and the second location. Thus, to get effective heat transfer the heat exchanger needs to have a larger design. Having a large heat exchanger can cause problems on aircraft where space and weight are limited.

SUMMARY

A heat exchanger includes a heat exchanger housing having a first flow path with a first inlet and a first outlet, and having a second flow path with a second inlet and a second outlet; a first fluid flowing from the first inlet to the first outlet in the first flow path, and a second fluid flowing from the second inlet to the second outlet in the second flow path; and a heat pipe array within the housing and extending between the first flow path and the second flow path for transferring heat from the first fluid to the second fluid.

A heat exchanger for use in gas turbine engines includes a first flow path for oil, a second flow path for fuel, and a plurality of heat pipes arranged in a matrix configuration. Each heat pipe includes a first end for contacting the oil in the first flow path and a second end for contacting the fuel in the second flow path, and a working fluid contained in a hollow cavity in the heat pipe to transfer heat between the oil and the fuel.

A method includes contacting first ends of a plurality of heat pipes in a heat pipe heat exchanger with oil, absorbing heat from the oil into the first ends of the heat pipes in the heat pipe heat exchanger, transferring heat from the first ends of the heat pipes to second ends of the heat pipes, contacting the second ends of the heat pipes with fuel, and releasing heat from the second ends of the heat pipes into the fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger utilizing heat pipes.

FIG. 2A is a perspective view of a first embodiment of the heat exchanger in a housing.

FIG. 2B is a perspective view of a second embodiment of the heat exchanger in a housing.

DETAILED DESCRIPTION

In general, the present invention relates to heat exchangers. Heat exchangers are used to transfer heat from a first location to a second location. Previously used heat exchangers utilizing shell and tube technology or plate and fin technology rely on convective heat transfer to move heat from the first location to the second location. Integrating heat pipes into a heat exchanger is advantageous, as the heat exchanger will be capable of transferring heat through both convective heat transfer and through phase-change heat transfer. The phase-change heat transfer occurs inside the heat pipes.

FIG. 1 is a perspective view of heat exchanger 10. Heat exchanger 10 includes wall 20 and heat pipes 22 (including heat pipe 22A, heat pipe 22B, heat pipe 22C, heat pipe 22D, heat pipe 22E, heat pipe 22F, heat pipe 22G, heat pipe 22H, heat pipe 22I, heat pipe 22J, heat pipe 22K, and heat pipe 22L). Each heat pipe 22 includes first end 24 (including first end 24A, first end 24B, first end 24C, first end 24D, first end 24E, first end 24F, first end 24G, first end 24H, first end 24I, first end 24J, first end 24K, and first end 24L) and second end 26 (including second end 26A, second end 26B, second end 26C, second end 26D, second end 26E, second end 26F, second end 26G, second end 26H, second end 26I, second end 26J, second end 26K, and second end 26L).

Heat exchanger 10 includes heat pipes 22 running through wall 20. Wall 20 provides support for heat pipes 22 and can also be used to separate two chambers when heat exchanger 10 is positioned for use. Wall 20 is a rectangular shaped wall in the embodiment shown in FIG. 1, but can be shaped to fit in any application in alternate embodiments. Wall 20 can have any thickness and size that is capable of being placed between two chambers and that is capable of supporting heat pipes 22. Wall 20 is made out of aluminum in the embodiment shown, but in alternate embodiments wall 20 can be made out of any conductive material that allows heat to transfer through wall 20 from the first chamber to the second chamber. Wall 20 can be manufactured with any suitable manufacturing process.

Heat pipes 22 are positioned in wall 20 with first ends 24 on a first side of wall 20 and second ends 26 on a second side of wall 20. Heat pipe 22A has first end 24A of a first side of wall 20 and second end 26A of a second side of wall 20; heat pipe 22B has first end 24B on a first side of wall 20 and second end 26B on a second side of wall 20; heat pipe 22C has first end 24C on a first side of wall 20 and second end 26C on a second side of wall 20; heat pipe 22D has first end 24D on a first side of wall 20 and second end 26D on a second side of wall 20; heat pipe 22E has first end 24E on a first side of wall 20 and second end 26E on a second side of wall 20; heat pipe 22F has first end 24F on a first side of wall 20 and second end 26F on a second side of wall 20; heat pipe 22G has first end 24G on a first side of wall 20 and second end 26G on a second side of wall 20; heat pipe 22H has first end 24H on a first side of wall 20 and second end 26H on a second side of wall 20; heat pipe 22I has first end 24I on a first side of wall 20 and second end 26I on a second side of wall 20; heat pipe 22J has first end 24J on a first side of wall 20 and second end 26J on a second side of wall 20; heat pipe 22K has first end 24K on a first side of wall 20 and second end 26K on a second side of wall 20; and heat pipe 22L has first end 24L on a first side of wall 20 and second end 26L on a second side of wall 20.

Heat pipes 22 can be any size and shape that is capable of being placed in wall 20. Heat pipes 22 each include a hollow housing. The housing can contain a working fluid that is capable of two-phase heat transfer and a wick material on interior surfaces of the housing to wick the working fluid from first ends 24 of heat pipes 22 to second ends 26 of heat pipes 22. Heat will enter heat pipes 22 at first ends 24 of heat pipes 22, causing the working fluid to vaporize. The vaporized working fluid can then be transferred through heat pipe 22. The vaporized working fluid can then release the heat from second ends 26 of heat pipes 22 into an ambient, causing the working fluid to condense. The wick material can then transfer the condensed working fluid back to first ends 24 of heat pipes 22. Heat pipes 22 can be constructed out of any suitable materials, including any suitable housing material, any suitable working fluid, and any suitable wick material.

Heat pipes 22 can be positioned in wall 20 after wall 20 has been manufactured. Wall 20 can be manufactured with apertures through which heat pipes 22 can be placed, or apertures can be formed in wall 20 after wall 20 is manufactured using any suitable manufacturing process, for instance drilling. In the embodiment shown in FIG. 1, heat pipes 22 are brazed into apertures in wall 20 to hold heat pipes 22 in place. In alternate embodiments, heat pipes 22 can be held in wall 20 with any means that will seal heat pipes 22 in wall 20 and prevent fluid from being passed from a first side of wall 20 to a second side of wall 20.

In the embodiment shown in FIG. 1, wall 20 holds twelve heat pipes 22 that are arranged in a matrix pattern. In alternate embodiments, wall 20 can hold any number of heat pipes 22 and heat pipes 22 can be arranged in any manner. The size, length, location, spacing, and number of heat pipes 22 in wall 20 can vary based on where heat exchanger 10 will be used.

Heat exchanger 10 is advantageous over previously used heat exchangers, as heat can be more efficiently transferred. Previously used heat exchangers transfer heat primarily with convective heat transfer between a first fluid and a second fluid. Convective heat transfer is limited in that there needs to be a large area of interface between the first fluid and the second fluid to effectively transfer heat. Thus, highly efficient heat transfer requires large heat exchangers to maximize the surface area at an interface between the first fluid and the second fluid.

Heat exchanger 10 is advantageous over previously used heat exchangers, as heat exchanger 10 transfers heat both through convective heat transfer and through phase-change heat transfer. Convective heat transfer occurs between a first side of wall 20 and a second side of wall 20 as fluid flows past wall 20 on both sides. Phase-change heat transfer occurs in heat pipes 22, as heat is transferred from first ends 24 of heat pipes 22 to second ends 26 of heat pipes 22. Having both convective heat transfer and phase-change heat transfer increases the effectiveness of heat exchanger 10. This allows heat exchanger 10 to be built smaller, as it will more effectively transfer heat. Having a smaller heat exchanger 10 is advantageous, as it reduces the weight of heat exchanger 10 and it reduces the space required to house heat exchanger 10. Reducing weight is advantageous for aircraft applications, as reducing weight will increase the overall effectiveness of the aircraft. Space is also limited on aircraft, thus reducing the amount of space required to house heat exchanger 10 is advantageous over previously used heat exchangers.

FIGS. 2A-2B show heat exchanger 10 in housing 30. FIG. 2A is a perspective view of a first embodiment of heat exchanger 10 in housing 30. FIG. 2B is a perspective view of a second embodiment of heat exchanger 10 in housing 30. Heat exchanger 10 includes heat pipes 22 with first ends 24 and second ends 26. Housing 30 includes first side 32, second side 34, third side 36, fourth side 38, first end 40, second end 42, first inlet 50, first outlet 52, first flow path 54, second inlet 60, second outlet 62, and second flow path 64.

Housing 30 is a hollow housing that is capable of holding heat exchanger 10. Housing 30 has first side 32 and second side 34 opposite each other, third side 36 and fourth side 38 opposite each other, and first end 40 and second end 42 opposite each other. Heat exchanger 10 is positioned in housing 30 so that wall 20 of heat exchanger 10 can be connected to first side 32, second side 34, third side 36, and fourth side 38 of housing 30.

When heat exchanger 10 is positioned in housing 30, two main chambers are formed with a first chamber on a first side of wall 20 and with a second chamber on a second side of wall 20. The first chamber on the first side of wall 20 has first inlet 50, first outlet 52, and first flow path 54. First flow path 54 extends through the first chamber from first inlet 50 to first outlet 52 and is capable of containing a first fluid that can flow through first flow path 54. The second chamber on the second side of wall 20 has second inlet 60, second outlet 62, and second flow path 64. Second flow path 64 extends through the second chamber from second inlet 60 to second outlet 62 and is capable of containing a second fluid that can flow through second flow path 64. In the embodiment shown, the first fluid is oil and the second fluid is fuel. In alternate embodiments, the first fluid and the second fluid can be any fluids that are capable of flowing through the first chamber and the second chamber, including but not limited to air, water, fuel, and oil.

As seen in FIG. 2A, first flow path 54 and second flow path 64 can be arranged so that the first fluid in first flow path 54 and the second fluid in second flow path 64 run parallel to each other. With this arrangement, first inlet 50 is located on first side 32 and first outlet 52 is located on second side 34. The first fluid will flow through flow path 54 from first inlet 50 to first outlet 52. In alternate embodiments, first inlet 50 and first outlet 52 can switch locations so that first inlet 52 is located on second side 34 and first outlet 52 is located on first side 32. This will cause the first fluid to flow in the opposite direction of what is shown. Also as seen in FIG. 2A, second inlet 60 is located on first side 32 and second outlet 62 is located on second side 34. The second fluid will flow through flow path 64 from first inlet 60 to first outlet 62. In alternate embodiments, second inlet 60 and second outlet 62 can switch locations so that second inlet 60 is located on second side 34 and second outlet 62 is located on first side 32. This will cause the second fluid to flow in the opposite direction of what is shown. Due to the flexibility in the design of housing 30, the first fluid and the second fluid can both flow in the same direction or in opposite directions depending on the arrangement of first inlet 50, first outlet 52, second inlet 60, and second outlet 62.

As seen in FIG. 2B, first flow path 54 and second flow path 64 can be arranged so that the first fluid in first flow path 54 and the second fluid in second flow path 64 run perpendicularly or crosswise to each other. With this arrangement, first inlet 50 is located on first side 32 and first outlet 52 is located on second side 34. The first fluid will flow through flow path 54 from first inlet 50 to first outlet 52. In alternate embodiments, first inlet 50 and first outlet 52 can switch locations so that first inlet 52 is located on second side 34 and first outlet 52 is located on first side 32. This will cause the first fluid to flow in the opposite direction of what is shown. Also as seen in FIG. 2B, second inlet 60 is located on third side 36 and second outlet 62 is located on fourth side 38. The second fluid will flow through flow path 64 from first inlet 60 to first outlet 62. In alternate embodiments, second inlet 60 and second outlet 62 can switch locations so that second inlet 60 is located on fourth side 38 and second outlet 62 is located on third side 36. This will cause the second fluid to flow in the opposite direction of what is shown. Due to the flexibility in the design of housing 30, the direction of flow of the first fluid in first flow path 54 and the direction of flow of the second fluid in second flow path 64 can vary depending on the arrangement of first inlet 50, first outlet 52, second inlet 60, and second outlet 62.

Heat exchanger 10 can also be positioned in housing 30 in a stacked configuration. This arrangement can take multiple forms. First, housing 30 can include multiple flow paths running through it, wherein one heat exchanger 10 is positioned in each flow path in housing 30. In this arrangement, the fluid will flow in a parallel manner through each separate flow path so that the fluid in a flow path only comes into contact with one heat exchanger 10 between the inlet and the outlet. Second, housing 30 can include one flow path but multiple heat exchangers 10 can be positioned along the flow path. In this arrangement the fluid will flow in a serial manner through the flow path to come into contact with each separate heat exchanger 10 between the inlet to the outlet. First flow path 54 and second flow path 64 can both include one heat exchanger 10 or a stacked configuration of heat exchanger 10. With a stack configuration, first flow path 54 and second flow path 64 can have the same stacked configuration or first flow path 54 and second flow path 64 can have separate stacked configurations so that one flow path has serial flow while the other has parallel flow. The exact positioning of heat exchangers 10 and design of housing 30 can vary based on different applications.

Heat pipes 22 are positioned in wall 20 to form heat exchanger 10. Heat pipes 22 have first ends 24 that extend into first flow path 54 between first inlet 50 and first outlet 52. Heat pipes 22 also have second ends 26 that extend into second flow path 64 between second inlet 60 and second outlet 62. Heat pipes 22 can transfer heat from the first fluid in first flow path 54 to the second fluid in second flow path 64 with phase-change heat transfer. This will effectively cool the first fluid and warm the second fluid. Heat pipes 22 should be sealed in wall 20 to prevent fluid crossover, and thus cross-contamination, of the first fluid in first flow path 54 and the second fluid in second flow path 64. Heat pipes 22 can be sealed in wall 20 by brazing, epoxying, or using any other suitable manufacturing process to seal them in place.

Each heat pipe 22 includes a hollow housing, a working fluid contained in the hollow housing, and a wick structure layer on the interior surfaces of heat pipe 22. The working fluid and the wick structure layer enable phase-change heat transfer through heat pipe 22. In the embodiment shown in FIGS. 2A-2B, the hollow housing of heat pipes 22 is made out of nickel plated copper tubes and the working fluid contained in the hollow housing is water. Using a nickel plated copper housing for heat pipe 22 is advantageous, as it has a higher conductivity than standard aluminum heat pipes. In alternate embodiments, the hollow housing can be made out of any suitable material and the working fluid can be any fluid that is capable of phase-change heat transfer.

Heat exchanger 10 can also include a maze or serpentine apparatus to direct the flow of the fluid in either first flow path 54, second flow path 64, or both first flow path 54 and second flow path 64. A maze or serpentine apparatus can be positioned around heat pipes 22 so that the fluid flows over each heat pipe one at a time or so that the fluid flows over a row of heat pipes 22 at a time. The design of the maze or serpentine apparatus can direct the flow back and forth through the flow path between the inlet and the outlet. Using a maze or serpentine apparatus increases the flexibility in the design of housing 30 and heat exchanger 10. The maze or serpentine apparatus could separate a flow path so that the inlet and the outlet could both be positioned on the same side of housing 30. Using a maze or serpentine apparatus can also increase the effectiveness of heat exchanger 10, as the maze or serpentine apparatus will create a more even flow through the flow path so that each individual heat pipe 22 can more effectively and reliably absorb and release heat from the fluid in the flow path.

In the embodiments seen in FIGS. 2A-2B, the first fluid in first flow path 54 is oil and the second fluid in second flow path 64 is fuel so that heat is transferred from the oil to the fuel. In a first alternate embodiment, the first fluid can be air and the second fluid can be fuel so that heat is transferred from the air to the fuel. In a second alternate embodiment, the first fluid can be oil and the second fluid can be air so that heat is transferred from the oil to the air. Transferring heat out of hot oil and transferring heat into cold fuel in a gas turbine engine is advantageous, as the oil needs to be cooled and the fuel needs to be heated. Oil is heated to high temperatures during use and needs to be cooled to protect components in the gas turbine engine from the undesirable effects of hot oil. Fuel enters the gas turbine engine cold and is heated during combustion. Being able to warm the fuel prior to using it for combustion is advantageous, as it allows the combustion process to happen quicker. Transferring heat from the hot oil to the cold fuel with heat exchanger 10 is mutually beneficial, as it will cool the oil and heat the fuel.

Heat exchanger 10 is further advantageous, as it allows heat to be efficiently transferred from the oil in first flow path 54 to the fuel in second flow path 64. Previously used heat exchangers only transferred heat through convective heat transfer. Introducing heat pipes 22 into heat exchanger 10 allows heat to be transferred with convective heat transfer and with phase-change heat transfer. Adding phase-change heat transfer to heat exchanger 10 allows heat exchanger 10 to be 10-100 times more thermally conductive than previously used aluminum heat exchangers.

Heat exchanger 10 is also more effective in heat transfer due to the placement of heat pipes in first flow path 54 and second flow path 64. First ends 24 of heat pipes 22 can extend any distance into first flow path 54. Second ends 26 of heat pipes 22 can extend any distance into second flow path 64. Placing first ends 24 and second ends 26 of heat pipes 22 into a center of first flow path 54 and a center of second flow path 64, respectively, allows heat exchanger 10 to contact more fluid in both first flow path 54 and second flow path 64 compared to previously used heat exchangers. How far first ends 24 and second ends 26 of heat pipes 22 extend into first flow path 54 and second flow path 64 depends on the size and shape of heat pipes 22 and the design of heat exchanger 10.

When designing heat exchanger 10 for a particular application, the size, shape, and placement of heat pipes 22 in first flow path 54 and second flow path 64 should be balanced to promote effective heat transfer while maintaining a proper pressure in first flow path 54 and second flow path 64. The pressure in first flow path 54 and the pressure in second flow path 64 will drop with the introduction of heat pipes 22, due to the existence of foreign objects in the pathway between first inlet 50 and first outlet 52 in first flow path 54, and between second inlet 60 and second outlet 62 in second flow path 64. The size, shape, and placement of heat pipes 22 should be designed so that the pressure in first flow path 54 and second flow path 64 is maintained at a level that continues to promote the flow of the first fluid and the second fluid through first flow path 54 and second flow path 64, respectively.

Overall, heat exchanger 10 is advantageous because it can more effectively and efficiently transfer heat from a first fluid to a second fluid. This increase in effectiveness of heat exchanger 10 means heat exchanger 10 can be designed with a smaller size and weight. When compared to previously used heat exchangers, heat exchanger 10 will have a minimum two times reduction in size for the same given heat transfer of a previously use heat exchanger. Having a smaller size and weight is beneficial in aircraft applications, as there are space and weight limits for aircrafts. Reducing the amount of space needed to house heat exchanger 10 allows heat exchanger 10 to be used in more applications where spaced is limited, compared to previously used models. Reducing the weight of heat exchanger 10 allows gas turbine engines in aircraft to function more efficiently, as the overall weight of the aircraft is being reduced.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A heat exchanger for transferring heat from a first fluid to a second fluid, the heat exchanger comprising: a heat exchanger housing having a first flow path with a first inlet and a first outlet, and having a second flow path with a second inlet and a second outlet; and a heat pipe array within the housing and extending between the first flow path and the second flow path for transferring heat from the first fluid flowing from the first inlet to the first outlet in the first flow path to the second fluid flowing from the second inlet to the second outlet in the second flow path.
 2. The heat exchanger of claim 1, wherein the first fluid is oil.
 3. The heat exchanger of claim 1, wherein the second fluid is fuel.
 4. The heat exchanger of claim 1, wherein the first fluid flows in a first chamber in the housing positioned between the first inlet and first outlet.
 5. The heat exchanger of claim 4, wherein the second fluid flows in a second chamber in the housing positioned between the second inlet and the second outlet.
 6. The heat exchanger of claim 5, and further comprising: a wall separating the first chamber from the second chamber in which the heat pipe array is held.
 7. The heat exchanger of claim 6, wherein the wall is made out of a conductive material to transfer heat from the first chamber to the second chamber.
 8. The heat exchanger of claim 1, wherein each heat pipe in the heat pipe array contains a working fluid that is capable of phase-change heat transfer.
 9. The heat exchanger of claim 8, wherein an interior surface of each heat pipe in the heat pipe array is covered with a wick structure layer to wick the working fluid.
 10. A heat exchanger for use in gas turbine engines, comprising: a first flow path for oil; a second flow path for fuel; and a plurality of heat pipes arranged in a matrix configuration, wherein each of the heat pipes comprises: a first end for contacting the oil in the first flow path and a second end for contacting the fuel in the second flow path; and a working fluid contained in a hollow cavity in the heat pipe to transfer heat between the oil and the fuel.
 11. The heat exchanger of claim 10, wherein the working fluid transfers heat through phase-change heat transfer.
 12. The heat exchanger of claim 10, wherein an interior surface of each of the plurality of heat pipes are covered with a wick structure layer.
 13. The heat exchanger of claim 10, wherein the plurality of heat pipes are held in a housing comprising: a first flow path in a first chamber with an oil inlet and an oil outlet; a second flow path in a second chamber with a fuel inlet and a fuel outlet; and a wall separating the first chamber from the second chamber in which the plurality of heat pipes is held.
 14. The heat exchanger of claim 13, wherein the first ends of the heat pipes are positioned in the hot oil flow path to absorb heat from the oil to cool the oil.
 15. The heat exchanger of claim 13, wherein the second ends of the heat pipes are positioned in the cold fuel flow path to release heat into the fuel to heat the fuel.
 16. A method comprising: contacting first ends of a plurality of heat pipes in a heat pipe heat exchanger with oil; absorbing heat from the oil into the first ends of the heat pipes in the heat pipe heat exchanger; transferring heat from the first ends of the heat pipes to second ends of the heat pipes; contacting the second ends of the heat pipes with fuel; and releasing heat from the second ends of the heat pipes into the fuel.
 17. The method of claim 16, wherein the oil is cooled as heat is absorbed from the oil into the heat pipes in the heat pipe heat exchanger.
 18. The method of claim 16, wherein the fuel is warmed as heat is released into the fuel from the heat pipes in the heat pipe heat exchanger.
 19. The method of claim 16, wherein the heat is transferred through the heat pipes in the heat pipe heat exchanger with a phase-change working fluid contained in each of the heat pipes.
 20. The method of claim 16, and further comprising: moving oil through a first chamber of the heat pipe heat exchanger positioned between an oil inlet and an oil outlet; and moving fuel through a second chamber of the heat pipe heat exchanger positioned between a fuel inlet and a fuel outlet. 